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GETIFADDRS(3) Library Functions Manual GETIFADDRS(3)

getifaddrs — get interface addresses

#include <ifaddrs.h>

int
getifaddrs(struct ifaddrs **ifap);

void
freeifaddrs(struct ifaddrs *ifp);

The () function stores a reference to a linked list of the network interfaces on the local machine in the memory referenced by ifap. The list consists of ifaddrs structures, as defined in the include file <ifaddrs.h>. The ifaddrs structure contains at least the following entries: 
    struct ifaddrs   *ifa_next;         /* Pointer to next struct */
    char             *ifa_name;         /* Interface name */
    u_int             ifa_flags;        /* Interface flags */
    struct sockaddr  *ifa_addr;         /* Interface address */
    struct sockaddr  *ifa_netmask;      /* Interface netmask */
    struct sockaddr  *ifa_broadaddr;    /* Interface broadcast address */
    struct sockaddr  *ifa_dstaddr;      /* P2P interface destination */
    void             *ifa_data;		/* Address specific data */

The ifa_next field contains a pointer to the next structure on the list. This field is NULL in last structure on the list.

The ifa_name field contains the interface name.

The ifa_flags field contains the interface flags, as set by ifconfig(8) utility.

The ifa_addr field references either the address of the interface or the link level address of the interface, if one exists, otherwise it is NULL. (The sa_family field of the ifa_addr field should be consulted to determine the format of the ifa_addr address.)

The ifa_netmask field references the netmask associated with ifa_addr, if one is set, otherwise it is NULL.

The ifa_broadaddr field, which should only be referenced for non-P2P interfaces, references the broadcast address associated with ifa_addr, if one exists, otherwise it is NULL.

The ifa_dstaddr field references the destination address on a P2P interface, if one exists, otherwise it is NULL.

The ifa_data field references address family specific data in a pointer to the struct if_data (as defined in include file <net/if.h>). For AF_LINK addresses, it contains various interface attributes and statistics. For all other address families, it contains per-address interface statistics.

The data returned by () is dynamically allocated and should be freed using () when no longer needed.

The getifaddrs() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

The getifaddrs() may fail and set errno for any of the errors specified for the library routines ioctl(2), socket(2), malloc(3) or sysctl(3).

ioctl(2), socket(2), sysctl(3), networking(4), ifconfig(8)

The getifaddrs implementation first appeared in BSDi BSD/OS.

If both <net/if.h> and <ifaddrs.h> are being included, <net/if.h> be included before <ifaddrs.h>.

November 25, 2014 FreeBSD-12.0